Debris clutters the sidewalk and street a block away from the site of a blast that leveled a strip club in Springfield, Mass.

Photo: Jessica Hill, Associated Press

Debris clutters the sidewalk and street a block away from the site...

Image 2 of 2

Inspectors stand in debris, Saturday, Nov. 24, 2012, at the site of a gas explosion that leveled a strip club in Springfield, Mass., on Friday evening. Investigators were trying to figure out what caused the blast where the multistory brick building housing Scores Gentleman's Club once stood. (AP Photo/Jessica Hill)

Photo: Jessica Hill, Associated Press

Inspectors stand in debris, Saturday, Nov. 24, 2012, at the site of...

A preliminary survey found that more than 40 buildings were damaged in a natural gas explosion that injured 18 people, building inspectors said Saturday.

A strip club was flattened and a day care center was heavily damaged in the huge explosion Friday night in Springfield, one of New England's largest cities. No one was killed in the blast.

Investigators tried to determine what caused the explosion that could be heard for miles, left a large hole in the ground where the multistory brick building housing Scores Gentleman's Club once stood, and scattered debris over several blocks.

Officials already had evacuated part of the entertainment district after responding to a gas leak and odor reported about an hour before the blast. Gas workers venting a leak got indications that the building was about to explode, and they ducked for cover behind a utility truck - along with firefighters and police officers - just before the blast, said Mark McDonald, president of the New England Gas Workers Association.

Most of the injured were in that group, and the truck that saved their lives was essentially demolished, he said.

"It really is a miracle, and it's an example of our public safety officials, each and every day, putting themselves in harm's way," said Stephen Coan, state fire marshal.

Officials also marveled how the 5:30 p.m. blast occurred when a day care center next door was closed. The center's building was heavily damaged.

Lt. Gov. Tim Murray and Springfield Mayor Domenic Sarno were attending a tree-lighting ceremony when the explosion occurred. Sarno said some people mistakenly thought the boom was part of the holiday event.

The explosion blew out windows in a three-block radius, leaving at least three buildings irreparably damaged and causing emergency workers to evacuate a six-story apartment building that was buckling, police said.

Authorities cordoned off the center of the explosion Saturday as building inspectors worked to identify unsafe structures. Anxious residents gathered at the perimeter, waiting for permission to visit their buildings.